This invention relates to roof/wall interface design for fire protection. In particular, it relates to a construction of roof intended for fire protection, and is mainly concerned with industrial and commercial buildings having a structural steel roof framework.
The invention is an exercise in structural fire control. It is concerned with preventing fire spread across the top of an internal wall or party wall in the space between said wall and the roof cladding, hereinafter called the walltop space. It is likewise concerned with protecting the structural integrity of the wall adjacent said walltop space in fire conditions.
The walltop space arises from the necessity of laying horizontal beams called purlins across the rooms of a building, supported by said internal walls or party walls and themselves carrying the roof cladding. The wall-plane section of a typical walltop space is a long rectangle defined by the roof cladding (the upper long side), the top of the wall (the lower long side) and a section of a purlin at either end (the two short sides).
It is known to seal the walltop space in fire-controlling manner by cutting or fabricating a curtain from a non-combustible material to fit said space, and disposing the curtain in the space, preferably inside a metallic supporting case, to form a firestop. The supporting case is needed when, as is commonly the case, the chosen non-combustible material is flexible, deformable or non-self supporting. Said material may be manufactured, for example, from spun fibres of volcanic and other rocks, treated with resin and cured to form a loose mat, commonly employed at a thickness of 50 mm and floppy at that thickness when bridging voids of dimensions exceeding about 30xc3x9730 cm. The preference for the supporting case arises not only from the last consideration but also to provide protection against damage from wear and tear in the course of building maintenance, services installation and repair, etc.
United Kingdom Patent specification no. GB 2 082 647 discloses a fire barrier for sealing a gap between a dividing wall and a roof of a building for preventing the spread of fire and smoke through the gap. The barrier comprises a body of channel section having side webs for securing the dividing wall. A gasket is secured in a fixing groove so as to abut the tiles to seal a gap. A fire break member is provided to join tiling laths where portions have been removed to prevent the spread of fire. Other fire break members to prevent the spread of fire across other structural members of the building are provided e.g. a channel section interconnects roof ridge portions and includes an internal plate for separating adjacent ends of the ridge portions.
The known walltop space seals are vulnerable, however, in fire conditions, to a hazard known as the fulcrum factor, according to which burning or heat-softened roof structures, especially purlins, collapse pivotally and act as levers to damage portions of the building hitherto unaffected by the fire, including the walltop space seal and adjacent wall portions, thereby opening channels for fire spread.
The invention seeks to create a roof structure offering effective containment of a fire outbreak occurring thereunder to a space defined by the walls of the room in which the fire started. It also seeks to create a fire-retardant roof structure wherein the danger of fire spread by the fulcrum factor aforesaid is substantially eliminated. A further object of the invention is to provide a roof structure for use in the cold or everyday form, which is continuous and stable, but which is capable of controlled separation in hot form or fire conditions, so as to compartmentalize the building and thus confine the fire.
The invention accordingly provides, in a building wherein a fire-resistant wall separates a first room from a second room and supports purlins which carry a roof cladding, a fire-retardant roof construction which is characterized in that it comprises
a first set of parallel purlins extending over said first room, each having one of its ends pivotally mounted about a horizontal axis parallel to said wall adjacent the top of the wall;
a set of upright cleats of sheet metal secured to the top of said wall, each providing the pivotal mounting for a respective purlin as aforesaid;
a second set of parallel purlins extending over said second room, and mounted on cleats in the manner of the first set;
the pivotal mountings being so located that each purlin, if deprived of support elsewhere, can collapse to hang down from its pivot without structural damage to the wall or the respective cleat;
a first respective fireproof curtain sealing the walltop space between each adjacent pair of purlins of the first set;
a second respective fireproof curtain sealing the walltop space between each adjacent pair of purlins of the second set;
the two curtains defining between them a sufficient space so that damage to one said curtain from collapsing purlins does not entail any breach of the other curtain; and
a divide in the roof cladding directly over said space, for controlled separation whereby the cladding can collapse together with its supporting purlins over one said room without effect on the purlins, or on the cladding supported by the purlins, of the other room.
In the specification, the word xe2x80x9croomxe2x80x9d is to be construed to include the situation where the xe2x80x9croomxe2x80x9d is a unit or bay in separate buildings as in industrial or commercial applications.
Preferably each cleat extends across the walltop to support two purlin ends, one in each room, on respective pivots. Thus the two sets of cleats referred to above are reduced, for preference, to a single set of double cleats.
End portions of a double cleat may, if desired, be offset mutually and united by a medial bridging member to increase the rigidity of the cleat. In that case the purlin ends are applied to opposite faces of the cleat.
Preferably the walltop space is additionally closed off in one or both rooms by a first decorative, and optionally fire resistant, wall cladding panel. Where the walltop is surmounted by a structural I-beam as is often the case, bridging members can be inserted between the flanges of the beam to present a rear edge to the beam web and a front edge, capable of accepting nails or screws, for application of a second wall cladding panel in addition. In fire conditions, the said first wall cladding panel will collapse with the failure of the adjacent purlins, but the said second wall cladding panel should not be affected, and will preserve the I-beam from the worst effects of the fire.
The invention will be understood in greater detail from the following description of a particular and preferred embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which